A typical drum brake parking brake and adjuster arrangement in common use for many years on automobiles manufactured in the United States and elsewhere is disclosed in U.S. Pat. No. 3,064,767, entitled "Brake Actuator" and issued on Nov. 13, 1962. That disclosure illustrates a duo servo drum brake assembly with the upper ends of the primary and secondary brake shoes being associated with an anchor pin, a hydraulic wheel cylinder which is pressure actuated for service brake operation, and a spreader bar forming a part of the parking brake actuating mechanism. Shoe retraction springs are also connected with the brake shoes and continually urge the shoe upper ends toward the anchor pin and to the brake release condition. The lower ends of the the brake shoes are connected through an adjuster strut having mating threaded sections, one of which may be rotated relative to the other to increase or decrease the effective length of the strut and therefore adjust the clearance between the braking surfaces of the primary and secondary brake shoes and the friction braking surface of the brake drum. A tension spring connecting both shoe lower ends maintains the shoes in engagement with the adjuster strut ends. The shoe-to-drum clearance is preferably maintained so as to permit the drum to rotate freely when the brake is released while keeping the distance that the shoes must be moved from the release position until they engage the drum when the brake is being actuated to an acceptable minimum distance. A parking brake actuating lever has one end pivotally mounted on the secondary brake shoe near the upper end thereof, an intermediate portion in engagement with one end of the spreader bar, and the lower end connected with a parking brake cable. This cable is tensioned to apply the parking brake, pivoting the parking brake actuating lever at its pivotally mounted end and moving the spreader bar against the primary brake shoe. The action and reaction forces exerted by the lever at the pivot on the secondary shoe and through the spreader bar to the primary shoe move the shoe upper ends outwardly and cause the shoe braking surfaces to engage the brake drum. Further tension force application through the brake cable applies additional braking force, actuating the parking brake to the desired extent.
This typical arrangement separates the adjuster mechanism from the parking brake mechanism. Like many other parking brake actuator mechanisms, it provides a parking brake actuating lever which is only a little shorter than the web of the secondary shoe on which it is mounted. That lever extends from a point adjacent the upper end of the secondary shoe to a point adjacent the lower end of that shoe in order to obtain the necessary lever ratio to provide brake actuating forces acting on the shoes. It requires clear space throughout its length within the brake assembly to accommodate its movements. When the brake assembly is provided with an automatic brake adjuster actuating mechanism, usually also mounted on the secondary shoe, the parking brake actuating lever competes with that mechanism for operational space.
U.S. Pat. No. 3,623,578, entitled "Combined Self-Adjuster and Parking Brake Actuating Mechanism" and issued Nov. 30, 1971, provides a self-adjuster mechanism in conjunction with the spreader bar of a leading-trailing drum brake assembly. Like U.S. Pat. No. 3,064,767 discussed above, the parking brake actuating lever is pivoted on the upper end of the trailing brake shoe and extends parallel to and immediately adjacent to the web of that brake shoe, terminating close to the lower end of the brake shoe where that shoe end engages the anchor. The parking brake actuating lever engages the spreader bar at a point intermediate the pivot point and the lever lower end, that point of spreader bar engagement being near the lever's pivot point. The parking brake cable is attached to the lever lower end fro parking brake actuation. Thus this arrangement requires the long actuator lever positioned parallel to and extending along most of the arcuate length of the shoe web, a spreader bar, and an adjuster mechanism associated with the spreader bar.
U.S. Pat. No. 4,344,512, entitled "Duo Servo Drum Brake and Parking Mechanism Therefor" and issued Aug. 17, 1982, has a construction generally similar to that of U.S. Pat. No. 3,064,767 noted above.
Another group of patent disclosures, exemplified by U.S. Pat. No. 4,051,928, entitled "Automatic Shoe Clearance Adjusting Device In Shoe Drum Brake" and issued Oct. 4, 1977; and U.S. Pat. No. 4,139,083, entitled "Adjusting Device For An Internal Shoe Drum Brake" and issued Feb. 13, 1979; relate to arrangements wherein the brake is adjusted during manual operation of the parking brake, with no adjustment being accomplished during service braking operations. Such arrangements leave the brake unadjusted unless the vehicle operator regularly uses the parking brake. With the typical automatic transmission now having a park capability which must be used to remove the ignition key, many operators do not also apply the parking brake. It is also a fact of life that in parking areas which are flat or have only a slight incline or decline, many vehicle operators almost never use the parking brake.
These disclosures include leading-trailing brake shoe arrangements. Each disclosure shows a combined spreader bar and adjuster, with the parking brake actuating lever being a toggle lever which is a part of a multi-part spreader bar. The lever lies in a plane parallel to the axis of rotation of the drum and also to the axis of the spreader bar main body. It is pivotally attached to the adjacent part of the spreader bar, and has one lever end near that point of pivotal attachment engaging a brake shoe to transmit parking brake actuating forces to that shoe with the pivotal reaction force being transmitted through the other parts of the spreader bar to the other brake shoe. The lever extends from its point of pivotal attachment in a direction substantially parallel to the drum axis of rotation and through the backing plate. It then is formed as a substantially right-angled elbow, with its other end located beyond the backing plate and outside the brake assembly envelope as broadly defined by the backing plate and the brake drum. The parking brake cable is attached to that other end and acts on the lever in a direction which is generally perpendicular to the elbow and the other end, that direction of action thus being generally parallel to the drum axis of rotation. These constructions require an adjuster/spreader bar arrangement located near but under the wheel cylinder, and an awkwardly extending parking brake actuating lever which has much of it located outside the drum brake assembly envelope. The lever does not have the advantages of being located in the drum brake assembly. The construction still requires a spreader bar.